Plants generally contain components, in particular also water-soluble components, such as sucrose, inulin or starch. These components are enclosed in plant cells and are separated by biological membranes which prevent cell juice from being able to exit. As a precursor for the extractive workup of cell material, it is therefore necessary to destroy these membranes so that the cell juice can escape. This, which is termed denaturation, of the plant material is customarily effected by heating the plant material to temperatures above 70° C. As a result the plant material is first heated and this denatured heated plant material is subsequently subjected to an extraction. This proceeds in such a manner that the extraction medium is passed in countercurrent flow to the cossette material, wherein the cossette material gives off the sugar and the extraction medium takes up the sugar. The extraction medium is generally colder than the plant material after the thermal denaturation. As a result, the temperature of the cossette material decreases along the extraction section, that is to say, the cossette material cools successively along the extraction section. According to the known extraction processes, the sugar beets processed into cossettes are heated as rapidly as possible to temperatures above 70° C. and extracted in countercurrent flow with the extraction medium, usually water, for example fresh water or condensate. As a result, a temperature gradient forms along the extraction section, which temperature gradient decreases after heating of the cossettes from the cossette feed up to the cossette discharge.
This procedure requires, however, that the extraction is carried out in a temperature range (65° C. to 75° C.) in which changes in the texture of the cossette framework substance and also chemical changes already occur on the cossette material. The consequence of this is that non-sugar components are extracted from the cossette material and the purity of the extract is decreased. At the same time, as a result of the high temperature, the texture of the cossette material is weakened. This is of importance, since generally the next processing step carried out is mechanical dewatering of the cossette material via, for example, twin-screw presses. The weakening of the cossette structure associated with the temperature stressing of the cossette material impairs the ability of the cossette material to be dewatered.